1. Field of the Invention
This invention relates to apparatus for controlling emissions from a metallurgical vessel and more particularly to an emissions control system having an improved movable hood structure for capturing emissions during charging of the vessel.
2. Description of the Prior Art
In the manufacture of steel utilizing a basic oxygen process, molten pig iron is poured from a ladle into the metallurgical vessel of a basic oxygen furnace (BOF) where the iron is refined by blowing oxygen onto its surface. During charging of the furnace, the vessel is rotated from its normal upright position employed during the refining or blowing process to a position in which the entrance to the vessel is spaced laterally from the conventional emissions processing equipment. Due to the extreme temperatures and large volume of emissions from the vessel during charging, they generally have not been effectively controlled during this portion of the steel making process. Rotating the BOF vessel to the charging position increases the distance from its mouth to the entrance of the conventional stationary emissions processing hood, allowing time for the emitted fumes to expand and entrain substantial volumes of ambient air which, combined with the lateral misalignment of the mouth of the vessel from the processing hood, makes collection more difficult and a substantial portion of such emissions have escaped into the surrounding atmosphere.
In the past, various attempts have been made to capture and control emissions during charging of a BOF. These attempts have included installation of expensive auxiliary emissions processing equipment with separate exhaust hoods and collectors adjacent to or surrounding the existing processing hood and equipment conventionally used during the refining process. Examples of such apparatus may be found in U.S. Pat. Nos. 3,844,745; 3,863,609; and 3,908,969. Such duplication of equipment not only adds substantially to the expense of producing steel, but also greatly complicates charging and tapping the furnace due to the congestion caused by the added equipment.
Another known means for controlling charging emissions is to construct an enclosure surrounding the metallurgical vessel in all its rotational positions. Such enclosure structures may be equipped with auxiliary emission exhausting and handling apparatus or may rely entirely upon the process equipment utilized during the refining process. Examples of enclosure structures utilized in connection with metallurgical vessels may be found in U.S. Pat. Nos. 3,743,264; 3,809,379; and 4,081,269.
It has also been proposed to provide a fume collecting hood structure which is movable with the metallurgical vessel whereby the fume collection apparatus is in position to collect emissions under any angular rotational position of the furnace, an example of this type of apparatus being disclosed, for example, in U.S. Pat. No. 3,844,769.
Attempts have also been made to control charging emissions from a BOF by attempting to induce the flow of the charging emissions into the existing process hood. One such device, shown in U.S. Pat. No. 3,854,709, employs a movable damper plate which is positioned over a major portion of the entrance of the process hood, leaving a small portion uncovered nearest the open mouth of the BOF vessel in the charging position. This reduced opening into the portion of the hood closest the BOF vessel mouth creates an increased velocity in this area to capture a greater portion of the emissions. While this apparatus is at least partially effective in that it is able to capture a larger portion of the emissions than would be captured by the existing process hood alone, an objectionable proportion of the emissions are still permitted to escape into the atmosphere.
Each of the emission control systems mentioned above have been at least partially effective in capturing emissions during charging of a BOF; however, these systems have not been entirely satisfactory for various reasons. Accordingly, it is a primary object of the present invention to provide an improved movable control hood for use in connection with existing process emission control systems to capture emissions from a BOF during charging.
Another object of the invention is to provide such a movable emissions control hood which is simple to operate and which occupies a minimum of space.
Another object of the invention is to provide such an improved movable emissions control hood which eliminates the necessity for auxiliary emissions processing equipment for providing effective capture of the emissions from a BOF when the vessel is moved from its normal upright blowing or refining position.